Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964999AbXASJII (ORCPT ); Fri, 19 Jan 2007 04:08:08 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S964998AbXASJII (ORCPT ); Fri, 19 Jan 2007 04:08:08 -0500 Received: from ecfrec.frec.bull.fr ([129.183.4.8]:51632 "EHLO ecfrec.frec.bull.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964999AbXASJIG (ORCPT ); Fri, 19 Jan 2007 04:08:06 -0500 Message-ID: <45B08B17.3060807@bull.net> Date: Fri, 19 Jan 2007 10:10:47 +0100 From: Nadia Derbey Organization: BULL/DT/OSwR&D/Linux User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.6) Gecko/20040115 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Hugh Dickins Cc: Franck Bui-Huu , LKML Subject: Re: unable to mmap /dev/kmem References: <45AFA490.5000508@bull.net> In-Reply-To: X-MIMETrack: Itemize by SMTP Server on ECN002/FR/BULL(Release 5.0.12 |February 13, 2003) at 19/01/2007 10:16:21, Serialize by Router on ECN002/FR/BULL(Release 5.0.12 |February 13, 2003) at 19/01/2007 10:16:24, Serialize complete at 19/01/2007 10:16:24 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=us-ascii; format=flowed Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1957 Lines: 48 Hugh Dickins wrote: > On Thu, 18 Jan 2007, Nadia Derbey wrote: > >>Trying to mmap /dev/kmem with an offset I take from /boot/System.map, >>I get an EIO error on a 2.6.20-rc4. >>This is something that used to work on older kernels. >> >>Had a look at mmap_kmem() in drivers/char/mem.c, and I'm wondering whether >>pfn is correctly computed there: shouldn't we have something like >> >>pfn = PFN_DOWN(virt_to_phys((void *)PAGE_OFFSET)) + >> __pa(vma->vm_pgoff << PAGE_SHIFT); >> >>instead of >> >>pfn = PFN_DOWN(virt_to_phys((void *)PAGE_OFFSET)) + vma->vm_pgoff; >> >>Or may be should I substract PAGE_OFFSET from the value I get from System.map >>before mmapping /dev/kmem? > > > Sigh, you're right, 2.6.19 messed that up completely. > No, you never had to subtract PAGE_OFFSET from that address > in the past, and you shouldn't have to do so now. > > Please revert the offending patch below, and then maybe Franck > can come up with a patch which preserves the original behaviour > on architectures which used to work (e.g. i386), while fixing > it for those architectures (which are they?) that did not. > > I guess it's reassuring to know that not many are actually > using mmap of /dev/kmem, so you're the first to notice: thanks. > I find this feature very interesting from a testing perspective. Now, since I don't like the idea of being the only one that uses a feature (not maintained - may be even to be removed?) may be you could advice me on a more broadly used way to get the value of a non exported kernel variable from inside a test running in user mode? should I use /dev/mem instead? But in that case, I should do the virtual to physical conversion myself, right? Regards, Nadia - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/